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RELATION OF DEHYDRATION 
TO AGRICULTURE 



By 
MAJ. S. C. PRESCOTT 

On Detail to Bureau of Chemistry for Dehydration Work 



Address before the National Association of Commissioners 

of Agriculture at Baltimore, Md. 

January 7, 1919 




UNITED STATES DEPARTMENT OF AGRICULTURE 

CIRCULAR 126 

OFFICE OF THE SECRETARY 



Washington, D. G. 



January 25, 1919 



WASHINOTON : GOVERNMENT PRINTING OFFICE : 1911 



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RELATION OF DEHYDRATION TO 
AGRICULTURE. 



THE four and one-half years through which we have just passed 
have, because of the war, caused us to study deeply the problems 
of food supply and food control. It has fallen to this country to be 
the storehouse from which enormous supplies of foods have been with- 
drawn for the use of the fighting forces and the civilian population of 
Europe. This demand upon our resources has been very largely for 
cereals and especially for wheat. Because of the necessity for send- 
ing enormous quantities of breadstuffs to the allies, the questions of 
conservation of food supplies have been studied with particular 
acuteness, and these studies have had their fruition in the movement 
for war gardens and for more careful preservation by canning, and 
particularly in the stimulation of drying as a means of protecting 
foods against spoilage and preserving them for future use. 

FOOD DRYING AN ANCIENT PROCESS. 

Drying has been known for hundreds of years and is probably the 
oldest method of food preservation which the human race has em- 
ployed. In our own country it was used in the early colonial days 
for both vegetable and animal foods. Massachusetts colonists dried 
corn after it had been cooked, the product being known as samp. 
As soon as fruits were produced, these, and especially the apple, were 
also dried in considerable quantities. Along the coast the drying of fish 
became an important industry, and throughout New England to the 
present time will be found the application of this process of food 
preservation as a sort of local or primitive industry. In other parts 
of the country other vegetables and fruits and meat products were 
dried. Peas and sweet corn may be mentioned as examples of the 
former, while along the Pacific coast the long sunny period lends 
itself particularly to the drying of prunes, raisins, and other fruits. 
In the arid regions of the interior the Indians, and later the early 
settlers, dried their beef or buffalo meat by cutting into thin strips 
and hanging up for the sun and wind to remove the excess moisture 
and sear over the outside with a protective coating which would 
prevent infection and spoilage. This was known as jerked .beef. 
Thus, long before the advent of canning on an extensive scale, the 
process of drying had been utilized in this country. In other 
countries it had doubtless been used for hundreds of years. 

101364°-18 Q 



4 RELATION OF DEHYDRATION TO AGRICULTURE. 

CANNING OF FOODS INTRODUCED INTO AMERICA. 

Approximately 100 years ago a new method of food preservation 
was introduced into America. This was the process of hermetically 
sealing in air-tight containers and subjecting to heat, It was brought 
to America from England, where it had been practiced for about 15 
years. The first patent on the preservation of food in air-tight con- 
tainers was granted in 1810 to a Frenchman, Appert, who inde- 
pendently discovered the method and utilized it in France. This 
process was brought to America by William Underwood, who, after 
tramping over the whole eastern section of the United States, finally 
settled in Boston and established a company for preserving foods by 
his process. 

The process of canning was at once seen to be so simple and so 
applicable to many kinds of food materials that it apparently com- 
pletely overshadowed the simpler process of drying. This was 
especially the case after the introduction of tinned "cans." Further- 
more, canned foods could be transported into any climate, be left 
exposed to the action of sun or rain, and so long as the container was 
intact the food, if perfectly sterilized, was properly conserved. The 
Civil War with its great Requirements of preserved foods for the 
armies gave a big impetus to the business, and later improvements 
in the methods of sterilization and in can making greatly increased 
the scope of the industry until we have the enormous industry of 
to-day. 

While this has been going on, there has been also a tremendous 
development in the preservation of foods by cold storage and by 
other physical means, such as pasteurization, salting, etc. With all 
the expansion along these lines, drying was practically forgotten, 
except on a domestic scale and in the dry valleys of the Pacific slope, 
where the fruits could be preserved very conveniently by this method 
by action of the sun. 

FIRST EXPERIMENTS IN DRYING POTATOES. 



At the time of the discovery of gold in the Klondike, the rush of 
miners to that district created a demand for foods which were light 
and could be easily transported, and dried potatoes imported from 
Germany were sold to the miners in considerable quantity. These 
were restored for use by soaking in water and could be served in 
the form of hashed or fried potatoes, and while they were not ex- 
tremely palatable, they did supply a quickly prepared and energy- 
giving ration for the hard-working miner. 

Noting the success of the German product, some attempts were 
made to manufacture dried potatoes in Oregon and Washington, but 
these were far from successful at first, because the manufacturers 



RELATION OF DEHYDRATION TO AGRICULTURE. 5 

used sulphur as a means of preventing the darkening of the slices of 
potatoes before drying, the amount of sulphur being entirely too 
great, with the result that the taste of the potato and the odor when 
cooking were very objectionable. This, however, was shortly over- 
come, and dried potatoes were manufactured in this country, though 
even this was far from modern dehydration. 

When we speak of " modern" dehydration to-day we mean foods 
which either with or without previous treatment have been sub- 
jected to the action of carefully regulated currents of air in which 
the temperature and humidity are both properly controlled and 
which results in the food product gradually losing water, but without 
giving up its color or flavor or having its cellular structure impaired. 
The modern dehydrated product, therefore, will absorb water again 
when placed in it, will swell to its normal size and appearance, and 
when cooked will have essentially the flavor, appearance, and odor 
of freshly cooked material made from the fresh vegetables. The 
early products were far from meeting these requirements, and the 
same is true of much of that made at the present time. When the 
White Fleet went on its famous voyage around the world, a large 
quantity of dehydrated vegetables was purchased for the use of the 
fleet. These were so objectionable as a result of improper methods 
of dehydration, which had produced blackening and scorching, that 
they were practically uneatable, and hundreds of pounds were 
thrown overboard. Not only was there a considerable loss at that 
time, but there was also created in the minds of the officers of the 
Navy a strong prejudice against any foods prepared by this method, 
a prejudice which has existed until the present day. However, 
progress was bound to come, and the best dehydrated products of 
the present day will meet every requirement which it is desired to 
impose upon them as regards appearance, flavor, and quality. 

THE DRYING INDUSTRY STIMULATED BY WAR. 

War seems to be a great stimulator of methods of food preserva- 
tion. Just as the Civil War stimulated the canning industry, so the 
Boer War, and, to a greater extent, the European war, stimulated 
the drying industry. During the Boer War the British Army in 
South Africa was supplied with thousands of pounds of dried vege- 
tables mixed so as to form the basis for a nutritious and quickly pre- 
pared soup. Much of this material was manufactured in Canada and 
shipped from Canadian or American points to South Africa. With 
the closing of the war, one of the manufacturers was left with several 
thousand pounds of such a soup mixture for which there was no local 
sale in the domestic markets, possibly owing to the fact that the aver- 
age consumer much preferred to buy vegetables in the fresh state, 
and possibly because the mixture was not ideal from the standpoint 



6 RELATION" OF DEHYDRATION TO AGRICULTURE. 

of flavor and palatability. However, this material was not thrown 
away, but was put up in barrels which were carefully paraffined and 
stored away. After the outbreak of the European war in 1914, they 
were sent to the British Army and utilized in the preparation of soups 
just as the bulk of the lot had been used 15 years before. I cite this 
as an example of the keeping quality of dehydrated products, pro- 
vided the conditions under which they are stored are satisfactory, 
and moisture and insect pests are prevented from gaining access to 
the food substances. 

BEGINNING OF THE DRYING INDUSTRY IN THE UNITED STATES. 

By 1910, a number of small factories had begun to manufacture 
the dehydrated vegetables and soup mixture in the United States. 
They had not proved highly satisfactory 7 from the commercial stand- 
point. However, the soundness of the fundamental principle was 
recognized, and improvement was then merely a matter of applying 
scientific methods and perfecting details. With the outbreak of the 
world war came a demand for more of these products for the use of 
the armies abroad, and thousands of tons were sent. With our own 
entrance into the war came the question of supplying these materials 
to our own forces. At first there was objection. Then came a 
willingness to purchase a small amount as an emergency supply of 
food materials, and finally, during the past year, there has been a 
demand for large quantities of these dried vegetables to take the 
place of the fresh vegetables which could not be obtained in sufficient 
quantity in England and France. The result is that during the past 
12 months many thousand tons of dried vegetables and soup mixtures 
have been purchased for the use of the American armies. 

Let us see how our oj>ponents in the war have taken advantage of 
this process. In 1898 there were three small dr}ung plants in Ger- 
many. Five years later there were still three plants there with an 
output large enough to be worth mentioning. This method of 
preservation may be regarded as apparently successful, for in 1906 
the number of plants in operation had increased to 39, in 1909 to 
199, in 1914 to 488, and in 1916 to 841. In addition to this, 2,000 
breweries were utilizing some portion of their equipment in the 
drying of food materials. It is stated that in 1917 about 1,900 
plants were in operation, or under construction, and the total quan- 
tity of potatoes alone dried in Germany was more than three times 
the total crop of the United States. These facts will explain one of 
the reasons why Germany was able to maintain her food supplies 
during the war. The German product was not as good as the best 
American product of to-day, and we have little reason to doubt, 
therefore, that if insistence is laid upon the high quality of the raw 






RELATION OF DEHYDRATION TO AGRICULTURE. 7 

material and the use only of the best methods, the dehydrated 
vegetable industry in the United States will develop at a rapid rate 
and become a powerful factor in the conservation movement and the 
stabilization of agricultural crons. 

DEHYDRATING SYSTEMS IN THE UNITED STATES. 

There are now in this country probably 25 small plants operating 
on dehydrated vegetables. Several methods are in use, but in all 
the fundamental principle is the same, namely, to remove the excess 
of water so as to obtain a product which will keep for a long period 
of time, which will not undergo spoilage as a result of microbic action 
or other form of chemical change, and which will conserve the food 
value of the materials intact. The methods now in use may be 
classified as follows: 

1. The tunnel systems. — These, as the name would imply, consist 
of long chambers or tunnels into which the prepared vegetables are 
introduced on screens or racks and through which a strong current 
of dry air is blown. There are a number of slight modifications 
in the arrangements of the screens and the method of heating and 
driving the air, but in the majority of cases the heat is supplied by 
extensive coils of steam pipe, and the air is forced through by means 
of powerful fans. In some instances the racks holding the vege- 
tables are placed on trucks which run on tracks, so that the material 
is introduced at one end and delivered in dry form from the other 
end. In other cases the tunnels have side entrances and the trays 
are inserted and removed by hand. The weak point of the tunnel 
systems lies in the fact that there is not absolute control of the 
physical conditions and as a result many vegetables, especially 
potatoes, are likely to be overheated and scorched, and more or less 
broken down in their cellular structure. 

2. Kilns. — The second type of plant may be described as kilns. 
These are based on the construction of the hop kiln as employed in 
California and Oregon and to some extent in New York State for the 
drying of hops and the evaporation of apples. They consist essen- 
tially of square chambers with sloping roofs and perforated floors, 
heated from below by means of stoves or furnaces. The vegetables 
to be dried are spread on the floor to a depth of 4 to 6 inches and the 
hot air from the stove passes up through the layer, taking away the 
moisture, which is conducted from the chamber through a ventilator 
in the roof. The material on the floor must be stirred up, or turned 
over, from time to time, and this is ordinarily accomplished by men 
with shovels. The products of the kilns are rather varied in char- 
acter. Some are quite satisfactory, while on the other hand others 
are very much overheated, or may go to the other extreme and be 
underdried. A lack of uniformity is therefore likely to be found in 
products of this method. 



8 RELATION OF DEHYDRATION TO AGRICULTURE. 

3. Vacuum process. — A third type is the vacuum process, which 
consists of closed chambers with large numbers of shelves heated by 
steam and with a greatly reduced atmospheric pressure. By the 
constant application of the vacuum to the process the water vapor 
is removed and the material dehydrated. This process gives excel- 
lent results for many kinds of products, but is rather severe and tends 
to break down the cellular structure. 

4. Special machines. — Special types of chambers or machines have 
been invented and are now in use in a number of places, the air 
passing through the chamber being conditioned so as to bring about 
a carefully regulated drying. Other special types of machines force 
the rapidity of drying, but have not the careful regulation which 
seems to be essential in the preparation of the finest products. As a 
result, therefore, it may be stated that only in those processes where 
we have the practically perfect control of temperature, humidity, 
and rate of air flow do we get products which will retain their color, 
appearance, and flavor, and when soaked in water will return to 
approximately the normal appearance. If the temperature is too 
high, overcooking takes place. If it is too low, the evaporation is 
insufficient and changes are likely to follow in the partially dried 
material. If it is too dry and too hot, destruction of the cellular 
structure is practically sure to follow. It is seen, therefore, that 
modern dehydration means the scientific control and coordination of 
the three factors of air, temperature, and moisture. 

ADVANTAGES OF DEHYDRATION. 

The advantages of dehydration are almost too obvious to require 
extended statement. Most evident of all is the loss in weight. All 
the vegetables in common use contain from 65 to 95 per cent of 
water. The dehydrated product made from these vegetables should 
contain from 5 to 10 per cent of water. There is, therefore, a very 
large reduction in weight and consequent saving in the transportation 
charges, which in general are based upon weight. 

Similarly there is a loss in bulk amounting to from 50 to 80 per 
cent of the bulk of the raw material. The importance of these factors 
to railroads in times of congestion such as we have just passed through, 
or to ships in overseas service, are very evident. In the mere matter 
of sending food to our armies abroad, one ship could easily carry the 
vegetable requirements which in the green or fresh state would take 
from 10 to 25 ships. 

From the standpoint of agriculture the greatest advantage of dehy- 
dration undoubtedly appears in the stabilization of crops and the 
conservation of materials. Under the present conditions we are 
confronted by either a feast or a famine. If we consider potatoes aa 
the most typical root crop, it is a matter of experience that a year in 



RELATION OF DEHYDRATION TO AGRICULTURE. 9 

which we get a very large harvest and consequently low prices is 
Mkeiy to be followed by a lean year with a small crop and high prices. 
This pendulum swing goes on decade after decade. With dehydra- 
tion the excess of the years of great yield can be stored up and made 
available in the following year when prices are higher and the crop 
much smaller. After a short time this would tend to equalize the 
amount of planting, and, other things being equal, to give us year by 
year a sufficient quantity of food materials at normal prices. 

The second great advantage is in the conservation of food materials. 
It is estimated that over 50 per cent of the fruits and vegetables 
grown in this country now never reach the consumer, as a result of 
poor transportation facilities, irregularities in marketing, or other 
causes. By making use of the process of dehydration, the second- 
quality materials could be preserved by drying and made available 
for human food and not allowed to rot and waste. Again, taking the 
potato as typical, those of class 2 and 3 (culls) could be used for the 
manufacture of dehydrated potato and potato flour, a product which 
has not yet received in this country the attention which it deserves, 
but which is now being manufactured to some extent in a number of 
different parts of the country. 

A third factor of importance in the relation of dehydration to 
agriculture lies in the fact that a better diversity of crops can be 
secured, and as a result of this there will be a good variety of the 
vegetables which are the equivalent of fresh materials available to 
poor and rich throughout the year. This means practically better 
feeding for the people at large, evening up of prices, and the pre- 
vention of famine or great food shortage as a result of poor crops in 
any particular location. 

COMMERCIAL DEHYDRATION STILL IN ITS INFANCY. 

The work in commercial dehydration is still in its early stages in 
this country. There are many problems yet to be determined. We 
are now attempting to find out which processes are best adapted for 
general use, whether dehydrated j)roducts are deficient in any of the 
nutritive principles which they should possess and which the fresh 
vegetables themselves possess, to work out satisfactory methods of 
storage and transportation by selecting the best types of containers, 
and to acquaint the consumer, especially in the cities, with the great 
advantages which are likely to be gained by the use of dehydrated 
products. 

Obviously, dehydration will succeed commercially only in those 
regions with abundant crops which can be contracted for at planting 
for a guaranteed price, or in centers having a short haul from the 
point of production and suitable shipping facilities. If, however, 
the problem is met scientifically there appears no reason to doubt 



10 RELATION OF DEHYDKATION TO AGKICULTURE. 

that a demand will be created and that dehydration will become, as 
canning has, a great industry of immense importance to agriculture, 
with the further advantage that no tin plate will be required and that 
the consumer will purchase practically nothing but food material, 
whereas in the purchase of canned foods he is buying and the rail- 
roads are shipping enormous quantities of water. 

In order to insure a successful industry, dehydrated products must 
have the quality which will make them the practical equivalent of 
the fresh materials. They must be handled in a sanitary manner, 
be put up in suitable packages, and sold at a price which will make 
them throughout the year comparable with fresh vegetables. We 
believe this can be done, and that dehydration will become the 
servant of agriculture as well as of the dwellers of the great cities. 









PUBLICATIONS OF THE U. S. DEPARTMENT OF AGRICULTURE 
RELATING TO THE PRESERVATION OF FOODS. 

AVAILABLE FOR FREE DISTRIBUTION BY THE DEPARTMENT. 

Home Canning by the One-period Cold-pack Method (Farmers' Bulletin 853). 
Home Canning of Fruits and Vegetables (Farmers' Bulletin 853). 
Home Preservation of Muscadine Grapes (Farmers' Bulletin 859). 
Homemade Fruit Butters (Farmers' Bulletin 900). 

Commercial Evaporation and Drying of Fruits (Farmers' Bulletin 903). 
A Successful Community Drying Plant (Farmers' Bulletin 916). 
Farm and Home Drying of Fruits and Vegetables (Farmers' Bulletin 984). 
Extension Course in Vegetable Foods for Self-instructed Classes in Movable School 
of Agriculture (Department Bulletin 123). 
The Raisin Industry (Department Bulletin 349). 

FOR SALE BY THE SUPERINTENDENT OF DOCUMENTS, GOVERNMENT 
PRINTING OFFICE, WASHINGTON, D. C. 

Canned Fruit, Preserves, and Jellies, Household Methods of Preparation (Farmers 
Bulletin 203). Price 5 cts. 

Evaporation of Apples (Farmers' Bulletin 291). Price 5 cts. 

Canning Vegetables in the Home (Farmers' Bulletin 359). Price 5 cts. 

Canning Peaches on the Farm (Farmers' Bulletin 426). Price 5 cts. 

Home Canning by One-period Cold-Pack Method (Farmers' Bulletin 839). Price 
5 cts. 

Drying Fruits and Vegetables in the Home, with Receipts for Cooking (Farmers' 
Bulletin 841). Price 5 cts. 

Methods Followed in Commercial Canning of Foods (Department Bulletin 196). 
Price 10 cts. 

Theory of Drying and Its Application to New. Humidity-regulated and Recircu- 
lating Dry Kiln (Department Bulletin 509) Price 5 cts. 



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